As telephone and communications infrastructure technology has evolved from the basic terrestrial wireline system, to the wireless cellular extension, and to the satellite-based global coverage enhancement, emphasis has been placed on enabling one user to communicate with another user. This communication can take the form of encrypted or unencrypted voice, paging information, audio-visual information, FAX data, and the like. The advancements in the wireless and satellite extensions to the basic wireline system enable users to communicate with each other from increasingly remote locations.
Parallel to these developments, have been advances in trunked radio systems. In a trunked radio system, a computer control unit establishes and manages a group channel which allows one user to talk while others listen. When a user wants to make a transmission, the computer assigns the radio to a transmit channel and assigns the other members of the group to a receive channel. As the trunk station receives transmissions from the users, they are repeated over the shared receive channel to the other members in the group. When the conversation has been completed or after the channel is idle for a period of time, the computer control unit directs the group members to return to a control channel thus allowing the communications channel to be used by another group. Trunked radio systems are used widely in public service sectors, such as police and fire departments, where coordination among several users is necessary to ensure timely and efficient response.
However, trunked systems are expensive to establish and maintain. To establish a group channel, at least one trunking station must be built to enable a line-of-sight communication link with each member in the user group. If the users are spread over a large geographical area, this may entail a network of repeater stations placed at the top of tall buildings, or hills in rural areas. The cost of establishing and maintaining this network can be very high.
Therefore, what is needed is a system that combines the geographical coverage of a global telephony system with the group channel capability of a trunked radio system.